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The Yukawa–Tsuno equation, first developed in 1959, [1] is a linear free-energy relationship in physical organic chemistry.It is a modified version of the Hammett equation that accounts for enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds.
The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system.
Helmholtz resonance, also known as wind throb, refers to the phenomenon of air resonance in a cavity, an effect named after the German physicist Hermann von Helmholtz. [1] This type of resonance occurs when air is forced in and out of a cavity (the resonance chamber ), causing the air inside to vibrate at a specific natural frequency .
The pEDA parameter (pi electron donor-acceptor) is a pi-electron substituent effect scale, described also as mesomeric or resonance effect. There is also a complementary scale - sEDA. The more positive is the value of pEDA the more pi-electron donating is a substituent.
Download as PDF; Printable version ... In physics, nonlinear resonance is the occurrence of resonance in a nonlinear ... (foldover effect). When the amplitude of ...
The Mössbauer effect, or recoilless nuclear resonance fluorescence, is a physical phenomenon discovered by Rudolf Mössbauer in 1958. It involves the resonant and recoil -free emission and absorption of gamma radiation by atomic nuclei bound in a solid.
Polar substituent constants describe the way a substituent will influence a reaction through polar (inductive, field, and resonance) effects. To determine σ * Taft studied the hydrolysis of methyl esters (RCOOMe). The use of ester hydrolysis rates to study polar effects was first suggested by Ingold in 1930. [6]
Field effects, F, are defined to include all effects (inductive and pure field). Likewise, effects due to resonance, R, are due to the average of electron-donating ability and electron-accepting ability. These two effects are assumed to be independent of each other and therefore can be written as a linear combination: